The demands of modern life require many mobile workers, students and business people to carry at least one electronic device to perform their daily work. Some of the more commonly utilized electronic devices are the pager, personal digital assistant “PDA”, the cellular telephone, the portable computer and a modem for the portable computer.
Portable computers are available in various models, functionality and costs from companies like Compaq, Toshiba, and Texas Instruments. Cellular telephones are available in various sizes, shapes, functionality and cost from companies such as Motorola, Nokia and Erricson. FIG. 1 illustrates a prior art cellular network 10 having a mobile cellular telephone exchange (MTX) switch 12 connected to a transceiver and antenna 14. A transceiver is located in each cell of the cellular network and communicates with the MTX to effect transmission and reception of signals to and from the mobile/portable telephone 16. The transceiver is typically connected to the cellular switch 12 via a leased or dedicated network line 18. The cellular switch 12 is typically connected to the land-based destinations via telephone network 20. FIG. 2 is a block diagram of the telephone network of FIG. 1. The hierarchical architecture of cellular switch 12 includes a central processing unit 22, memory 24, data storage disk 26, cellular interface 28 central office trunk interface 30 and a backplane or switching matrix 32.
While hand held cellular telephones have become increasingly popular with the public over the last few years, very few hand held cellular telephones presently incorporate internal modems or ports for connecting to stand alone modems since cellular telephones have rarely been used to transmit data due to problems associated with transmitting data in a mobile environment. Numerous errors are induced into data transmission because of problems associated with cellular telephone communication. Echo and fading problems cause multiple bit errors in the data stream, and such problems occur frequently with a moving vehicle. For example, the transmitted signal may hit a building or other obstacle and bounce erratically or fade as the vehicle is shielded from the cell antenna. This high frequency of error in the data stream transmitted by cellular transmission renders the error correction protocol present in conventional wire line modems unsuitable for cellular use. Errors occur so frequently in a cellular environment that the number of repeat requests becomes large and data transmission efficiency is reduced below an acceptable amount. In some instances, errors may occur so often that a correct packet may never be received. Thus, the error correction protocol present in conventional telephone modems is unable to cope with problems presented in a cellular environment.
One solution to the problem of transmitting data in a vehicle mounted cellular telephone environment is discussed in U.S. Pat. No. 4,697,281 to O'Sullivan, herein incorporated by reference. The patent describes a cellular telephone data communication system and method involving the use of a mobile data processing interface and a cooperating static data processing interface to effectively transmit data over a cellular telephone system. Each data processing interface includes a processor which operates in the transmitting mode to add an error control correction data format to data received from an external data source. The data is divided into packets and provided to a modem which is uniquely operated to eliminate the action of the modem scramble system and remain active in spite of a carrier signal loss. The modem is deactivated or disconnected by a disconnect signal from the processor, and when carrier signal loss occurs, this disconnect signal is provided only after the lapse of a delay period without the resumption of the carrier signal. The error control correction data format causes a receiver to evaluate the received data for error and to retransmit an acknowledgment signal, the processor will again provide a data packet of received data. In the absence of an acknowledgment signal, the processor will again provide a data packet to the modem for retransmission. Also, the processor will determine the frequency of error in the received data from the acknowledgment signals and subsequently adjust the data packet size in accordance with this error frequency.
The portable computer disclosed in U.S. Pat. No. 4,697,281 is connected to the mobile data programming interface via a cable connected to an RS 232 interface in the mobile data programming interface, as illustrated in FIG. 3. The cable or tethered connection is fine as long as there is little movement between the portable computer and the mobile data programming interface and as long as the cable does not interfere with movement of a cellular telephone user. The problems of mobility and portability be more accurate it when the mobile phone is a hand held or portable cellular unit. Mobility is inhibited since a user of the hand held or portable cellular telephone can only move up to the distance of the cable or tethered connection from the portable computer, and when moving, the user must separately carry the portable telephone and the portable computer. Portability is inhibited since the cable or tethered connection must be removed and reattached each time the components are separated a distance greater than the cable or tethered connection. Additional problems include tripping over the cable or tethered connection, catching the cable or tethered connection on furniture, cut cables or tethered connections and worn out cable connections.
The same can be said for a telecommunications system that uses a cellular telephone, tethered to a portable computer, to transmit data. FIG. 4 illustrates a portable telephone 16 (cellular in the present case) having an external interface 34 that facilitates external electrical access to portable telephone 16. FIG. 5 illustrates an exposed side view of portable telephone 16. External interface 34 provides external electrical access to individual or various combinations of voice signal line(s), data signal line(s), command and/or control signal line(s), etc., depending upon the design and capability of the portable telephone 16. And while the external interface 34, as illustrated in FIG. 4, is a fourteen contact connector on the bottom surface of portable telephone 16, it could just as easily be located at a different location on the telephone, have fewer or more electrical contacts, or be an assortment of individual electrical contacts not part of a connector. The electrical contacts of interface 34 can be accessed individually (typically by test equipment or as a whole with a mating connector when coupling portable telephone 16 via an electrical cable 36 to another apparatus, such as a portable computer 38, as illustrated in FIG. 6.
Thus, while the invention of U.S. Pat. No. 4,697,281 and the telecommunications system illustrated in FIG. 6 offer partial solutions problems associated with transmitting data in a cellular telephone environment, they fail to remedy mobility and portability problems caused by a cable or tethered connection between a portable telephone and a portable computer.